Annales Geophysicae (Sep 2014)

On the man-made contamination on ULF measurements: evidence for disturbances related to an electrified DC railway

  • U. Villante,
  • U. Villante,
  • A. Piancatelli,
  • A. Piancatelli,
  • P. Palangio

DOI
https://doi.org/10.5194/angeo-32-1153-2014
Journal volume & issue
Vol. 32
pp. 1153 – 1161

Abstract

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An analysis of measurements performed at L'Aquila (Italy) during a deep minimum of solar and magnetospheric activity (2008–2010) allowed for the evaluation of possible contamination of the ultralow-frequency (ULF) spectrum (f ≈ 1–500 mHz) from artificial disturbances, practically in absence of natural signals. In addition, the city evacuation and the interruption of all industrial and social activities after the strong earthquake of 6 April 2009 allowed also for the examination of possible changes of the contamination level under remarkably changed environmental conditions. Our analysis reveals a persistent, season-independent, artificial signal, with the same characteristics in the H and Z components, that affects during daytime hours the entire spectrum; such contamination persists after the city evacuation. We speculate that the DC electrified railway (located ≈ 33 km from the Geomagnetic Observatory of L'Aquila, it maintained the same train traffic after the earthquake) is responsible for the observed disturbances.